feat(ci): optimize Molecule VM creation

- reuse validated runner-owned Vagrant linked-clone masters\n- create the default guests in bounded two-machine batches\n- capture create timing and runner utilization diagnostics

.github/scripts/monitor-runner-resources.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+
+set -Eeuo pipefail
+
+output_dir="${1:?output directory is required}"
+interval="${2:-10}"
+[[ "$interval" =~ ^[1-9][0-9]*$ ]] || {
+  printf 'monitor interval must be a positive integer\n' >&2
+  exit 2
+}
+
+mkdir -p -- "$output_dir"
+umask 077
+
+free -h > "$output_dir/memory-before.txt"
+df -h > "$output_dir/disk-before.txt"
+vmstat -w "$interval" > "$output_dir/vmstat.txt" &
+vmstat_pid=$!
+
+iostat_pid=""
+if command -v iostat >/dev/null 2>&1; then
+  iostat -dx "$interval" > "$output_dir/iostat.txt" &
+  iostat_pid=$!
+else
+  printf 'iostat is not installed on this runner\n' > "$output_dir/iostat-unavailable.txt"
+fi
+
+cleanup() {
+  local rc=$?
+  trap - EXIT INT TERM
+  kill "$vmstat_pid" 2>/dev/null || true
+  [[ -z "$iostat_pid" ]] || kill "$iostat_pid" 2>/dev/null || true
+  wait "$vmstat_pid" 2>/dev/null || true
+  [[ -z "$iostat_pid" ]] || wait "$iostat_pid" 2>/dev/null || true
+  free -h > "$output_dir/memory-after.txt"
+  df -h > "$output_dir/disk-after.txt"
+  exit "$rc"
+}
+trap cleanup EXIT INT TERM
+
+while :; do
+  sleep 3600 &
+  wait $!
+done